Xander: Well, this is new territory for me. I mean, my valentines are usually met with heartfelt restraining orders.Buffy: She’ll love it.Xander: I wish dating was like slaying, you know? Simple, direct, stake to the heart, no muss, no fuss.[Vampire shoots out of grave, attacks Xander, gets slayed by Buffy.]Buffy: Sorry to say, Xand. Slaying is a tad more perilous than dating.Xander: Well, you’re obviously not dating Cordelia.

Wikipedia’s synopsis:

In this episode, Cordelia breaks up with Xander after her friends mock her. Xander retaliates by attempting a love spell to „put her through the same hell“, and he gets a little more than he had bargained for.